Mixers are often used for front end receivers for a wireless handset such as a cell phone. A mixer is used to convert received radio frequency signals to a lower frequency for easier signal processing. The mixer is also referred to as a frequency converter. An important requirement for a mixer is its lineary. Although active mixers have been used, such as those incorporating the Gilbert cell topology, passive mixers which have no gain are often used because of their high linearity and low noise when compared to the active mixers. However, passive mixers often need an input gain stage, which contributes to a non-linear response of the mixer.
Attempts to address such linearity problems include the use of a resistance load within the gain stage amplifier. However, resistance values may vary during integrated circuit fabrication as well as vary with temperature. Thus, the output DC voltage of the resulting amplifier may be both process and temperature dependent, which is undesirable.
Highly linear amplifiers are also desirable in contexts other than as an input gain stage to a passive mixer.